Shear Conditioning Promotes Microvascular Endothelial Barrier Resilience in a Human BBB‐on‐a‐Chip Model of Systemic Inflammation Leading to Astrogliosis

The blood-brain barrier (BBB) maintains cerebral homeostasis and protects the central nervous system (CNS) during systemic inflammation. Advanced in vitro models integrating circulation, a functional BBB, and reactive glial cells are essential for studying the link between peripheral inflammation and neuroinflammation. Fluid shear stress, a key hemodynamic parameter, strengthens microvascular barriers. This study examines endothelial shear conditioning on barrier function in a fluidic µSiM-BBB (Microphysiological System featuring a Silicon Membrane -BBB). hiPSC-derived brain microvascular endothelial cell monocultures are conditioned with 0.5 Pa shear stress for 48 h. Shear conditioning lowers baseline permeability, increases glycocalyx production, and reduces responses to inflammatory challenges, including barrier breakdown, ICAM-1 upregulation, and neutrophil transmigration. Shear conditioning produces a resilient barrier function against a low-dose inflammatory challenge (10 pg mL^-1 TNF-α/IL1-β/INF-γ) but a high-dose challenge (50 pg mL^-1) disrupts the barrier. Adding astrocytes as neuroinflammatory "sensors" reveals that a high-dose inflammatory challenge activates astrocytes but only in combination with fibrinogen-a plasma protein known to trigger astrogliosis in multiple neurological conditions. This study highlights the utility of fluidic-enabled µSiM-BBB for investigating acute peripheral inflammation and brain injury relationships, serving as a foundation for more advanced models, including more cells of the neurovascular unit and brain parenchyma.